Due to the increasing exhaustion of the currently exploited oil deposits (petroleum hydrocarbons), oil prospection efforts are presently tending towards extreme places. In this connection, the Arctic Ocean and its marginal seas, the Arctic shelf regions, and the Arctic permafrost regions, which are assumed to contain about 25% of the world's oil and gas reserves, are also increasingly moving into the focus of interest. In some places, oil is already being extracted in significant amounts.
The central Arctic Ocean is covered throughout the year with sea ice, which can be thick in some areas. In the Arctic marginal seas and the shelf and coastal regions, drift ice or a closed sea-ice cover is present at least during the colder seasons of the year. Extraction platforms which are set up in these regions are subject to particular loads caused by drifting ice. Another problem is material fatigue caused by very low temperatures. This is true, for example, for the submarine pipelines that lead to the anchorage sites of the ships in the shelf region. Transporting oil through the ice by ship also involves increased risks, so that the risk of oil contamination or ship accidents is much higher in this region than in temperate or tropical latitudes. In polar ice regions, in addition to single oil spills caused, in particular, by ship or other accidents, there is also a high risk of continuous oil spills, which may be caused, for example, by oil extraction from platforms, or during loading operations for oil transports, or by leaks in burst-prone pipelines.
The oil removal measures so far employed in free water can only be used to a limited extent in polar ice regions, because the distribution of oil in ice differs significantly from that in water. Only frazil ice behaves similarly to water. A problem in the development of methods for oil removal in sea ice-covered regions lies in the different ice conditions. There is no uniform ice cover, and therefore no method which could be generally used in ice. Ice conditions vary from ice platelets, frazil ice, young pancake ice, and larger ice floes, up to a closed ice cover. The measures for ice removal are not only dependent on the consistency of the ice and the floe size and thickness, but also on the dynamics of the ice field, on the weather, and on the swell of the water between the floes. The oil slick may get under the ice or smeared over the ice floes, be frozen into the ice, or mix homogeneously with the frazil ice. Generally, it can be said that the separation of oil and ice becomes very difficult once the oil gets into the ice. It is still easier if the oil concentrates between ice floes in the water, but even then it is not possible to use all of the methods usually used in water, because most equipment (e.g., oil barriers) cannot be maneuvered in areas of ice floes.
To date, no minor or major spills are known to have occurred in sea ice-covered regions. However, since the risk of oil spills is on the rise and the natural cleansing capacity of these ecosystems is known to be significantly lower than in other places because of the very low temperatures prevailing there, it is becoming increasingly urgent to develop effective measures and methods for cleaning up oil spills in sea ice-covered areas. The current state of the art in the field of oil spill recovery in ice-covered areas is described extensively in a report of July 2004 issued by the ARCOP project of the European Union (ARCOP D4.2.1.1 (a), Chapter 4 “Oil spill response—present alternatives for ice covered water” pp 29-88). The report presents possible methods (see below) and their advantages and disadvantages. Some of the presented methods and tools have been tested in small studies, but have not yet been used in emergency situations.
Mechanical methods, which all amount to a kind of “washing principle”, make up the major part of the proposed oil removal methods. However, these methods are only suitable for cleaning smaller ice floes. Oil residues remain in the ice. In all mechanical schemes, the biology of the environment is severely affected, in most cases even completely destroyed. Regeneration occurs at a very slow pace.
Burning of oil in ice, which is generally referred to as “in-situ burning”, is a method which can only be used either when the degree of ice coverage is low or when it is very high. The oil content in the ice must exceed 25 percent in order for the oil to burn off The removal of oil is fast and effective. This method has the disadvantage that the heat produced completely destroys the ecosystem, so that afterwards there is hardly any chance for residual contamination to be eliminated by natural biological degradation. Moreover, the emissions and combustion residues may have toxic effects even at places relatively far from the burning site.
Chemical methods are of limited suitability for use in ice due to the lack of effective mixing, which is only possible if a small number of ice floes are in turbulent water. Moreover, many of the chemical dispersants are toxic and, therefore, most of them are forbidden in Germany. Besides, the oil is actually not removed; rather, the problem is merely displaced, because dispersed oil can spread more easily.
Biological methods can theoretically be used in ice. However, to date, they have not been used in practice, because experts consider it impossible for oil to be effectively biodegraded at the low unphysiological temperatures in ice. A small population of hydrocarbon degraders could, in fact, be identified in the ice; but these were only short-chain alkane degraders (B. Gerdes et al. “Influence of crude oil on changes of bacterial communities in Artie sea-ice”, FEMS Microbiology Ecology 53 (2005) pp 129-139). Inoculation of oil degraders in ice is also problematic because the temperature and salinity conditions are not only extreme, but also highly variable.
In general, biological methods, also known as bioremediation methods, are very environmentally friendly, and are frequently used in prior art methods in warmer areas, especially for soil clean-up purposes. Such methods promote the development of the natural, oil-degrading microbial community by adding nutrients to compensate for the lack of nitrogen and phosphates, thereby accelerating the natural degradation process. To date, this technology has been successfully used not only in soils but also in near-coast waters, and even in cold waters, for example during the Exxon Valdez disaster in the Arctic waters off the coast of Alaska. Apart from the addition of nutrients, experiments were also conducted on the addition of oil-degrading bacteria. To date, however, this inoculation method has proved successful only in closed systems or containers (ex-situ methods, for example for cleaning up excavated soils), but not in free nature. When types of bacteria were used which normally do not live in the contaminated place, such bacteria were mostly unable to compete with the specific, well-adapted autochthonous flora (Zhu et al. “Literature review on the use of commercial bioremediation agents for cleanup of oil-contaminated estuarine environments”, EPA report no. EPA/600/R-04/075 July 2004). Also, generally only a single type of hydrocarbon-degrading bacteria was used, for example one of the genus Pseudomonas (DE 38 11 856 C2), Bacillus (DE 196 52 580 A1), or Acetobacter (DE 44 43 266 A1). In the most favorable case, the degradation was accelerated for a short period of time. After about 2 weeks, the inoculated organisms were grown over with autochthonous flora.
In Japanese abstracts JP 2004181314 A and JP 200607542 A, it is proposed to use natural bacterial mixtures for soil clean-up purposes. However, unlike sea ice, soils are relatively homogenous and stable habitats, in which organisms are not exposed to a physical-chemical gradient as strong as that in sea ice. In addition, the introduced bacteria cannot be washed out so easily. Furthermore, European document EP 0 859 747 B1 discloses a method for aerobic biodegradation of substances having low water solubility. This method uses a culture of the thermophilic microorganism designated IHI-91 (DSM 10561). This strain is very similar to the genus Bacillus. The scope of protection of this European patent encompasses the microorganism IHI-91 itself and the enzyme composition obtainable therefrom for biodegradation purposes. The document DE 196 52 580 A1 referred to earlier herein does, in fact, mention a “bacterial mixture” for regenerating soils and waters contaminated by crude oil and/or oil products. In addition to the bacterial genus Bacillus, there is also used an unspecific “biosurfactant BS-4”, which is produced by hydrolysis of micro-biomass (waste). It is not clear whether additional types of bacteria are contained therein. However, due to the strong chemical hydrolysis, it can be assumed that the mixture contains only one bacterial genus. Finally, German document DE 199 54 643 A1 discloses the manufacture and use of an oil binder for removing all kinds of oils and fats from water surfaces and solid surfaces. Microorganisms are immobilized on fiber-forming proteins in granular form. These microorganisms may be of the type Pseudomonas putida, Pseudomonas spec., Acinetobacter calcoaaceticus, Nocardia spec., Corynebacterium spec., Candida lipolytica, Candida tropicalis, Rhodopseudomonas palistris or Rhodococcus spec. It is not described whether bacterial mixtures are immobilized. Also, no specific information is provided concerning the selection of the microorganisms mentioned. The immobilization of microorganisms is not included in any of the exemplary embodiments described.
All of the aforementioned publications have in common that they describe the biological degradation of oil by bacteria of different genus and species only at normal or even elevated ambient temperatures (thermophilic bacteria), but not at low temperatures (by definition, cold-adapted bacteria are organisms that have a minimum growth temperature of 0° C. or lower; the group of cold-adapted organisms being further dividable into what is known as “psychrophilic organisms”, which have a maximum growth temperature below 20° C., and the “psychrotolerant organisms”, which have a maximum growth temperature above 20° C. German document DE 10 2005 028 295 A1 describes only the use of psychrophilic proteases of the genus Shewanella for removing biofilms from hard surfaces. However, none of the applications described is for the low temperature range around or below the freezing point. Rather, it can be assumed that the use of psychrophilic proteases is aimed at shifting the temperature at which dirt and biofilms are removed from the previously used value of 37° C. to a range between 15 and 20° C. (see paragraphs [006] through [008]). It is not disclosed to remove biofilms under sea-ice conditions.
Sea ice with its extremely low temperatures and highly varying salinities is a hostile environment, which is considered by experts to be unsuitable for bioremediation methods. The only bioremediation experiment in sea ice so far published is that of DeIiIIe et al. (“Seasonal Variation of Bacteria in Sea Ice Contaminated by Diesel Fuel and Dispersed Crude Oil”, Microb. Ecol. (1997) 33 pp 97-105). Antarctic sea ice was contaminated with Arabian crude or diesel oil, and some of the experimental areas were fertilized with the organic nutrient complex INIPOL EAP 22. An increase in microorganisms was observed both in the fertilized and also in the unfertilized oil-contaminated experimental areas as compared to the control area. However, it was not examined whether and to what extent oil had been degraded, or which components had disappeared. The organisms that were present after the distribution of oil and nutrients were not isolated or characterized. However, the increase in microorganisms suggests that the oil at least does not have a toxic effect on part of the sea-ice community.
As mentioned earlier, the hostile conditions in sea ice, i.e., the very cold temperatures and sometimes very high salinities, and the strong variations in temperature and salinity across the ice floe profile and over the season, stand in the way of using bioremediation methods in such regions. Even in cold-adapted bacteria, microbial growth and activity are low in the temperature range from about −5° C. to −3° C., which is the temperature range prevailing in the lower region of the ice (boundary region between water and ice), and in the region of the ice surface (temperature range from about +1° C. in summer to below −20° C. in winter), microbial growth and activity are even limited to the short summer season. Sea ice is colonized by a specific microbial community which is closely adapted to the particular environment in which they live. Since polar sea ice has so far scarcely been confronted with crude oil, experts have so far considered it quite improbable that a natural, hydrocarbon-degrading flora could occur and quickly develop in the event of an oil spill. On the one hand, these factors speak against the use of bioremediation methods in ice but, on the other hand, it is especially in sea ice that biological methods offer many advantages over physical-chemical methods. They could be used in virtually any ice situation and oil spill scenario, regardless of whether the oil is on the ice, under the ice, or in free water. Moreover, once the nutrients and organisms were applied, they would need no further attention. Thus, it would not be necessary to stay at the site during oil spill recovery operations in difficult-to-access areas. Rather, the system could be left alone once it has been prepared.
The prior art has not proposed any practical bioremediation methods for degrading oil in sea ice regions (see ARCOP D4.2.1.1 (a), Chapter 4 “Oil spill response—present alternatives for ice covered water” pp 29-88 , at page 88, chapter 5.6). However, B. Gerdes et al. (WP4 Environmental Protection, “Biological degradation of crude oil in Artic sea ice”, ARCOP Workshop 8, 19-20 Oct. 2005, St. Petersburg) describes the possibility of a bioremediation method allowing natural aerobic degradation processes in polar ice regions to be accelerated by bioaugmentation with exogenous microbes and/or addition of nutrients and/or oxygen. Among the degradation-limiting factors mentioned are nutrients, availability of oxygen, temperature, trace elements, such as iron, salinity and pH value, solubility and droplet size of the oil. However, it turned out oil was not able to be significantly degraded during the Arctic winter at temperatures around −3° C., either by fertilization with nutrients, or by inoculation, whereas the bacterial diversity changed significantly at 0° C. in inorganically fertilized melt water samples.
Thus, B. Gerdes et al. (WP4 Environmental Protection, “Biological degradation of crude oil in Artic sea ice”, ARCOP Workshop 8, 19-20 Oct. 2005, St. Petersburg), discloses that a bioremediation method for accelerated biological degradation of petroleum hydrocarbons in polar ice regions by bioaugmentation with exogenous, hydrocarbon-degrading bacteria and addition of nutrients is possible at temperatures above the freezing point. It appears that the biodegradation stops below the freezing point. However, no information is provided on the mode of operation of the bioremediation method or on suitable bacterial mixtures as means for carrying out the method.